Desiccant reactivation

Calculate the desiccant reactivation heating and cooling requirements. 

Fortran Programs for Chemical Process Design Desiccant Reactivation... 

Desiccants can lose water capacity and drying efficiency by taking up moisture during storage. They should therefore be analy2ed before use. If necessary, the materials should be reactivated (regenerated) before putting them in service. 

Desiccant replacement is another operating cost, although desiccant life is usually several years in regenerable appHcations. Desiccant life depends on the stabihty of the desiccant in the given service, the frequency of regeneration, the presence of reactive contaminants, and the possibiUty of upsets to normal operation. 

A high-ieniperature heater to provide hot regeneration gas to reactivate the desiccant in the towers. 

Adsorption is the property of certain extremely porous materials to hold vapors in the pores until the desiccant is either heated or exposed to a drier gas. The material is a solid at all times and operates alternately through drying and reactivation cycles with no change in composition. Adsorbing materials in principal use are activated Alumina and silica gel. Molecular sieves are also used. Atmospheric dew points of minus 1000°F are readily obtained using adsorption. 

Silica gel and activated alumina present few practical problems. They are easily reactivated after use by heating in a ventilated oven, to 130-300°C for silica gel, and 150-700°C for activated alumina. British standard specifications have been published for desiccants for packaging which regulate the contents of soluble chloride and sulphate, dust content and absorptive capacity. 

Switzerland, and prepared according to a literature procedure, were used by the submitters without any noticeable difference. Lead tetraacetate was dried prior to use for at least 12 hours over potassium hydroxide and phosphorus pentoxide in an evacuated desiccator (12 mm.) that was protected from direct light. If well protected from moisture, lead tetraacetate can be kept for weeks in this way. However, after exposure to moisture in the air, lead tetraacetate usually turns brown from hydrolysis to lead hydroxide. The reactivity of such lead tetraacetate is diminished somewhat, but it can still be used. If the lead tetraacetate has turned black, the reagent should be recrystallized from glacial acetic acid and dried prior to use as described above. 

The free radical damage hypothesis of desiccation injury requires that these various protective mechanisms are unable to detoxify reactive species during dehydration and rehydration. There is evidence that free radicals increase with decreasing moisture content of seeds (Priestley et al., 1985), and, in plants subjected to episodic droughting, increased levels of malon-dialdehyde occur (Price Hendry, 1987). 

Sodium azide Heavy metals, 4758 Sulfuric acid Hydrofluoric acid, 4479 Vinyl acetate Desiccants, 1532 See ASSESSMENT OF REACTIVE CHEMICAL HAZARDS... 

Zinc Benzenediazonium Chloride. C6H5N NG-ZnCl2,C6HsN2Cl3Zn mw 276.87 N 10.12% solid. A self-reactive compd which has been known to expld after 15 hrs storage in a vac desiccator... 

NaBH4 is degraded by reaction with moisture in the air. Therefore it should be kept in a desiccator. To check that NaBH4 is reactive, take a drop of NaBH4 solution and add one small drop of glacial acetic acid, which should... 

Determine percentage moisture content (see Chapter Al). Alternatively, if sample is limited, accurately weigh 0.5 to 2 g sample into an aluminum container and dry 20 hr at 80°C. Cool in a desiccator containing recently reactivated absorbent and weigh again. Calculate moisture content as ... 

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